A technique for the light microscopy of tissues fixed for fine structure

Young adult female rats were perfused with buffered aldehydes. Selected tissues were prepared for light microscopy by standard techniques. The only procedural modifications permitted were those required by the special physical and chemical characteristics of the tissue. Extreme brittleness called for special precautions in all manipulative steps from excision to final embedment. Turbulence during the early stages of dehydration was lessened by drop‐by‐drop addition of the next concentration of ethanol. High melting‐point paraffins and celloidin‐paraffin embedments were used to accommodate the hardness of the tissues and to prevent disarrangement during mounting. Steel knives specially sharpened with fine abrasives on plate glass were fitted with fluid reservoirs. Four micron sections were obtained routinely. Sections were transferred individually from the reservoir to glass slides. The common dyes used in light micoscopy tended to overstain these tissues. This tendency was overcome by using shorter exposure times, lower concentrations and blocking agents. The chromatic staining techniques familiar to histologists and pathologists were useful after minor modifications.